1. Field of the Invention
The invention relates to data players in which a reading and/or writing head is positioned relatively to a data medium being read and/or recorded.
2. Description of the Related Art
A data player and/or recorder is a device which allows to read data stored on a data medium. The data may represent software for a computer, music or movies. Any other kind of data may be considered, either digital or analog.
The data medium may for example be a magnetic, optical or magneto-optical data carrier.
Many types of data players and/or recorders are commonly known. Some of these use tape shaped carriers, others use disk shaped carriers. The data is read from and/or written to the data medium using a data reading and/or writing head.
The data may for example be found along tracks. Typically a data medium carries a plurality of parallel tracks. To read and/or write data in a track the reading and/or writing head is positioned relatively to the track For some operations it may be necessary to read and/or write data in a distant part of a track separated from the part of the track being read by a plurality of parallel tracks.
More precisely and as may be seen in the side view contained in FIG. 1, in case the data player is an optical disk player 1 the data is stored on a disk 2 along tracks which describe concentric rings or a spiral. The data reading head 3 is an optical pick-up unit and is positioned relatively to a track to be read such that a laser beam 4 attains the track. The data reading head 3 may be moved, for example along a radial direction 5 of the optical disk 2 from a first position A to a second position 8 such that the laser beam 4 accesses data at the location B distant from the track being read at the location A. The distant location B and the location A are typically separated by a number of neighbored tracks. The data reading head 3 is moved using a driving unit. The driving unit may for example comprise a motor 6 which rotates an endless screw 7 oriented in the radial direction 5. The data reading head 3, comprises a nut shaped part (not shown) which cooperates with the endless screw 7 in a manner that when the endless screw 7 is rotated, the data reading head 3 moves in the radial direction 5. The position of the data reading head 3 is determined using an encoder 7E which delivers signals when the endless screw 7 is rotated. Depending on a way of rotations of the endless screw 7 the signals may cause a counter to increment or decrement a position value. The position value is used to determine the position of the data reading head 3. Many other ways of determining the position are well know by a person skilled in the art and could have been used instead of the encoder 7E described.
U.S. Pat No. 4,977,539 discloses a compact-disk player in which the optical pickup's position is determined using an encoder. The optical pickup is moved from a first to a second position which are separated by a number of tracks. Typically the optical pickup has a fixed speed of movement. The number of tracks is converted to a target number of encoder signals. While the optical pickup is moved the encoder signals are counted and compared to the target number. As soon as the number of encoder signals is equal to the target number a reverse direction braking is applied to the optical pickup. At this point the optical head passes beyond the second position and needs to be repositioned back in a direction reverse to it's first direction of movement in order to reach the second position. The higher the fixed speed, the stronger the reverse direction braking needs to be in order to brake the optical head and to position it back to the second position. This drawback in fact limits a movement's speed and thus an access time to go from the first position to the second position.